On the possibility of ground-based direct imaging detection of extra-solar planets: The case of TWA-7

Abstract

We show that {\em ground-based} direct imaging detection of extra-solar planets is possible with current technology. As an example, we present evidence for a possible planetary companion to the young T Tauri star 1RXSJ104230.3$-$334014 (=TWA-7), discovered by ROSAT as a member of the nearby TW Hya association. In an HST NICMOS F160W image, an object is detected that is more than 9 mag fainter than TWA-7, located $2.445 \pm 0.035^{\prime \prime}$ south-east at a position angle of $142.24 \pm 1.34^{\circ}$. One year later using the ESO-NTT with the SHARP speckle camera, we obtained H- and K-band detections of this faint object at a separation of $2.536 \pm 0.077^{\prime \prime}$ and a position angle of $139.3 \pm 2.1^{\circ}$. Given the known proper motion of TWA-7, the pair may form a proper motion pair. If the faint object orbits TWA-7, then its apparent magnitudes of H=$16.42 \pm 0.11$ and K=$16.34 \pm 0.15$ mag yield absolute magnitudes consistent with a $\sim 10^{6.5}$ yr old $\sim 3$ M$_{\rm jup}$ mass object according to the non-gray theory by Burrows et al. (1997). At $\sim 55$ pc, the angular separation of $\sim 2.5^{\prime \prime}$ corresponds to $\sim 138$~AU. However, position angles and separations are slightly more consistent with a background object than with a companion.